This invention relates to gasifier systems and methods for the efficient conversion of solid fuels to usable heat energy.
The prior art is best exemplified by U.S. Pat. No. 5,284,103 entitled BIO-MASS BURNER CONSTRUCTION by Hand et al, which is a division of U.S. Pat. No. 5,178,076 entitled BIO-MASS BURNER CONSTRUCTION issued Jan. 12, 1993 to the same inventors. In these patents, the burner utilizes a first burning chamber having a falling fuel entrained bed zone positioned above a traveling grate having a porous metallic woven belt. Primary air is directed through the porous belt to establish an oxygen-starved first burning chamber. A second burning chamber in fluid communication with the first burning chamber has a restricted diameter and effectively provides a hot-air gas nozzle. In larger sized units, a plurality of conveyors constitutes the traveling grate with the conveyors being arranged in head-to-head stepped relationship so that unburned fuel received by gravity from the entrained bed zone is agitated or jostled to enhance its burning.
According to the present invention, firebelts ensure that the heat loss from heating unnecessary air is minimized. The quantity of air at each point in the combustion process is stringently controlled. This air control benefits the combustion process in three ways:
First, by minimizing the heat loss of the combustion process, this minimizes the amount of carbon monoxide which is produced. Carbon monoxide, a priority pollutant, is produced directly proportional to the combustion temperature. Therefore, by minimizing excess air, the quantity of carbon monoxide produced is minimized.
Secondly, nitrogen oxides, another priority pollutant, is produced by combining the nitrogen in the air with the oxygen in the air. This combination of nitrogen and oxygen only occurs at high temperatures. The higher the temperature, the greater the quantity of nitrogen oxides that are produced. While the combustor of the present invention utilizes high temperatures, the formation of nitrogen and oxides is minimized since there is no excess oxygen to combine with the nitrogen. All the oxygen is used in the combustion process.
Thirdly, by minimizing the amount of air supplied to the combustion process, the amount of energy required to move air to the combustor is minimized. Electrical energy costs are typically 20% less than similar combustion systems where the air is not stringently controlled.
A further feature of the present invention is in the use of reflected infrared energy. Heat is a form of electromagnetic energy similar to light where the rays can be refracted or reflected. Radiation produced from heat is of a longer wavelength than visible light and is called infrared rays. By reflecting a certain amount of the heat produced from a combustion process, this invention is able to supply heat to the gasification process. The reflected heat will be of benefit in two ways:
Firstly, the heat is reflected to a point where the heat can be used to assist the combustion process. This is generally where the fuel first enters the combustion process. At this point, the fuel must be heated and the water removed. These processes require addition of energy which can be added for heat of the combustion of a part of the fuel or from the reflected energy. Using a part of the fuel to preheat the remaining fuel is inefficient, leaving less total heat available for production of electricity. Using reflected heat removes or minimizes this inefficiency. The second way this benefits the overall combustion process is in that the energy is transferred in a beneficial wayxe2x80x94not wasted by irradiating and heating in the combustion chamber. Heat that is absorbed by the combustion chamber is generally wasted since there is no direct benefit from this radiation. A small portion is used in the maintenance of the necessary combustion temperature but the majority of irradiating heat is wasted as low-level heat irradiating from the combustor exterior. Reflective heat added to the fuel will benefit the overall combustion efficiency, and this is a feature of the present invention.
Another feature of the invention is that the speed of the conveyor drive and the rate of inlet air and the control of inlet air is much more closely controlled so as to achieve high efficiency. Still another feature of the invention is that the fuel feed ramping is based on thermal conditions at the boiler output.
Still another feature of the invention is that the induced draft fan control is based on the draft pressure and boiler airflow rate.
Still another feature of the invention is in the method to control catalyst feed levels based on pollutant levels in the stack as measured at a continuous emission monitoring system point.
Finally, the invention features a control system which is based on operational parameters sensed at different stages in the process.
Accordingly, the object of the invention is to provide an improved gasifier system.